1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an array substrate for a LCD device and fabricating method thereof.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, much effort is being made to research and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs) as substitutes for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and facing each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a perspective view of an LCD device according to the related art. As shown in FIG. 1, the LCD device 11 includes an upper substrate 5, a lower substrate 22 and a liquid crystal 14. The upper substrate 5 is referred to as a color filter substrate that includes color filter patterns 8, a black matrix 6 between the color filter patterns 8, and a common electrode 18 on both the color filter patterns 8 and the black matrix 6. The lower substrate 22 is referred to as an array substrate that includes a data line 15 and a gate line 13 that cross each other and define a pixel region P. A pixel electrode 17 and a thin film transistor T as a switching element are positioned in each pixel region P. Thin film transistors T, which are disposed adjacent to the crossings of the data lines 15 and the gate lines 13, are disposed in a matrix on the lower substrate 22. The gate line 13 and a storage electrode 30 overlapping the gate line 13 define a storage capacitor C.
In the process of attaching the color filter substrate to the array substrate of FIG. 1, misalignment may occur thereby causing light leakage. Due to the possibility of misalignment during attachment, the black matrix is formed with a margin of error to compensate for the possible misalignment. Thus, an aperture ratio of the LCD device is reduced.
FIG. 2 is a cross-sectional view of a color filter-on-transistor (COT) LCD device according to the related art. As shown in FIG. 2, in a COT LCD, a display region D and a non-display region ND are defined.
In the display region D, a lower substrate 40 includes a thin film transistor T having a gate electrode 42, a semiconductor pattern 44, and source and drain electrodes 46 and 48. The array substrate further includes a black matrix 54 and color filter patterns (R and G) 52a and 52b. The black matrix 54 corresponds to the thin film transistor T. The color filter patterns (R and G) 52a and 52b include red color filter pattern (R) 52a, green color filter pattern (G) 52b and blue color filter pattern (not shown) corresponding to respective pixel regions P. A pixel electrode 56 is disposed in each pixel region P. In the display region D, an upper substrate 70 includes a common electrode 72. To maintain a gap between the lower and upper substrates 40 and 70, a spacer 80 is disposed between the lower and upper substrates 40 and 70. In the non-display region ND, a light-shielding portion 74 is disposed on the upper substrate 70 to shield leakage of light.
In order that the black matrix 54 disposed on the lower substrate 40 prevents reflection of light, the black matrix 54 should have a permittivity no less than 3.0. However, since the generally used black matrix has carbon as a main ingredient, it does not act as insulator. Accordingly, only a small amount of carbon is added to reduce a permittivity. Here, the black matrix having a small amount of carbon does not shield incident light. Therefore, in the non-display region ND, a separate light-shielding portion 74 is disposed on the upper substrate 70.
However, in the related art COT LCD, the number of separate processes to form the light-shielding portion increases, thereby increasing production cost. Additionally, a margin for attaching the upper and lower substrates is needed, and misalignment during attachment can occur.